Image forming devices move media sheets along a media path. The media sheets initially begin at an input area that is sized to hold a stack of sheets. Each sheet is individually picked from the stack and introduced into the media path. The media path comprises a series of roller nips, guides, and/or belts. The sheets move along the media path and through an imaging area where an image is transferred to the sheet. The media sheet is then either output from the device, or recirculated through a duplex path for receiving an image on a second side.
Media sheets are moved from the input area and into the media path in a timely manner. The distance between sheets moving along the media path is preferably minimized to increase the overall throughput of the device. The device throughput is the number of media sheets that receive a toner image and are outputted from the device within a given time period. Higher throughput devices are usually preferred by users.
The timing for moving a media sheet from the input area varies depending upon the height of the media stack. When the stack is full, the distance the media sheet moves before entering the media path is small. As the stack is depleted, the distance into the media path increases. Compensation is necessary to maintain a minimum inter-page gap as the stack height is reduced.
The movement of the media sheets from the input area and along the media path should occur without media jams or print defects. Media jams require the user to determine the location of the jam, access and remove the jammed sheet(s), and restart the image formation process.
Movement of the media sheets is also important to prevent print defects. Print defects occur when the media sheet is not properly aligned when moving through the imaging area. Misalignment may occur in the scan directions (i.e., left and right), as well as the process directions (i.e., forward and backward).